Conventionally, induction heating of a metal belt or metal sheet and such has been executed by an induction heating apparatus of a solenoid coil equipment type or a transverse coil equipment type.
However, in the case of induction-heating of a metal sheet with an intermediate-frequency power supply of 50 Hz to 1000 Hz by this induction heating apparatus, it is necessary to configure a magnetic circuit having a relatively small magnetic resistance. This is because the larger the magnetic resistance is, the lower a power factor becomes so that heating efficiency becomes worse.
In addition, in the induction heating of a metal sheet by the conventional induction heating apparatus, there is a problem that temperatures at both ends in a direction (width direction) orthogonal to a conveying direction of the metal sheet are suppressed from rising so as to remain low. In particular, in an induction heating apparatus of a hydraulic pressurizing type for feeding out an object to be heated while the object to be heated is pressurized with hydraulic pressure, it is difficult to circulate a magnetic flux generated outside a seal structure part of the hydraulic pressure by a coil, and this results in a problem that the temperature of the metal sheet positioned outside the seal structure part is lowered so as to be defective. Note that an object to be heated is referred to as a “heating target object,” hereinafter.